Hi Marten! I have developed a patch for memcached 1.4.x that splits memcached's slab store into metadata and data bits, so that the key/values can live on flash without a tremendous performance penalty. Ultimately, I predict the best solution will be to use the storage engine branch and/ or Northscale's membase, but for the time being the patch works pretty well. I'll send you a private email with more info.
thanks! Mitch (from Fusion-io) On Jul 9, 10:01 am, Marten Lehmann <[email protected]> wrote: > Hello, > > I know that memcached is designed to get its speed from the fast > access to RAM. But RAM is still very expensive - even with the amount > of RAM you get for the same money increasing every year. > > When I thought of using PCIe SSDs instead of RAM I wasn't doing this > with regard to persistence of objects. I just noticed, that the Fusion- > io's ioDrives are working with near-RAM speed, having the PCIe bus as > the only bottleneck in speed (don't mix it up with SATA SSDs). An > ioDrive 160 GB with SLC memory is available for less than $6,000 and > is capable to perform more than 100,000 random IOPS (read and write), > whereas with ECC RAM you'd have to pay a multiple of that amount the > get the same ressources. > > I don't know of any way to use a block device (like the ioDrive) as > RAM, you can only use RAM as a block device (which doesn't help in > this situation). So for the emerging market of PCIe SSDs (many high > performance databases are using this as replacement for RAID 10 arrays > and large RAM) it would be necessary to extend or branch memcached to > support SSD block devices. > > Did someone start with that, is this possibly already on the roadmap, > or did the maintainers refuse to extend memcache with this option for > a reason? > > Btw.: We are using memcached in conjunction with nginx as a web proxy > to our backend webservers to cache images and other static files, > which improves performance a lot. But 64 GB of RAM is much more > expensiv than 160 GB of an ioDrive PCIe SSD. > > Kind regards > Marten
